ir       ^  — 

B-H 


UNIVERSITY  OF  CALIFORNIA 

COLL!  GE  OF  DENTISTRY 


EXTENSION  LECTURES 


UC-NRLF 


172    13D 


HAND -CARVED  PORCELAIN  SHELL  AND 
OTHER  CROWNS,  TOGETHER  WITH 
AMALGAM  MODEL  TECHNIQUE  FOR 
CROWNS  AND  INLAYS. 


BY 

Dr.  GEO.  L.  BEAN 

Professor  of  Dental  Porcelain,  College  of  Dentistry,  University  of  California 


JANUARY  3-7,   1916 


pr 


GIFT   OF 


UNIVERSITY  OF  CALIFORNIA 

COLLEGE  OF  DENTISTRY 


EXTENSION  LECTURES 


HAND -CARVED  PORCELAIN  SHELL  AND 
OTHER  CROWNS,  TOGETHER  WITH 
AMALGAM  MODEL  TECHNIQUE  FOR 
CROWNS  AND  INLAYS. 


BY 

Dr.  GEO.  L.  BEAN 
i< 

Professor  of  Dental  Porcelain,  College  of  Dentistry,  University  of  California 


JANUARY  3-7,  1916 


UNIVERSITY  OF  CALIFORNIA  PRESS 

BERKELEY 

1916 


tit 


LIBRARY 


HAND-CARVED  PORCELAIN  SHELL  AND  OTHER  CROWNS, 

TOGETHER  WITH  AMALGAM  MODEL  TECHNIQUE 

FOR  CROWNS  AND  INLAYS 


HISTORY 

Porcelain  shell  or  jacket  crowns  are  by  no  means  new.  The  literature 
of  dentistry  for  the  last  twenty-five  years  devotes  considerable  space  to 
their  construction  and  use. 

In  the  Dental  Cosmos,  Dr.  Capon  of  Philadelphia  and  others  have  re- 
ported periodically  their  success  with  these  crowns,  and  at  no  time  have 
they  receded  from  their  favorable  opinion  of  them. 

The  original  work  and  development  of  this  type  of  restoration  was 
done  by  Doctor  Land  of  Detroit,  many  years  ago,  and  later  modified  by 
Doctor  Land  and  Doctor  Spaulding  into  what  has  become  known  as  a 
porcelain  shell.  This  is,  essentially,  a  crown  baked  on  a  platinum-foil 
matrix,  which  foil  is  later  removed  and  the  crown  cemented  over  a 
conical-shaped  tooth  stump.  The  work  for  many  years  was  largely  con- 
fined to  peg-shaped  lateral  incisors,  except  in  the  hands  of  a  few  men, 
but  since  the  search-light  of  the  X-ray  has  been  thrown  upon  our  root 
fillings  and  the  dental  and  medical  professions  have  demonstrated  sys- 
temic lesions  that  may  arise  from  poorly  treated  and  improperly  filled 
roots,  there  has  arisen  throughout  the  country  a  demand  for  methods  of 
operative  procedure  that  will  save  vital  pulps  whenever  possible. 

It  is  probable  that  the  reason  the  porcelain  shell  never  came  into 
popular  use  was  that  there  are  technical  difficulties  associated  with  its 
proper  construction.  The  method  about  to  be  illustrated  was  developed 
with  the  idea  of  eliminating  the  uncertainties  of  handling  porcelain  in 
these  delicate  restorations,  and  so  making  it  possible  for  the  general 
practitioner  of  dentistry  to  handle  this  work  as  regular  routine,  rather 
than  to  send  his  patient  to  a  specialist. 

WHERE  INDICATED 

(a)   On  a  peg  or  rice-shaped  laterals. 

(&)  Badly  broken  down  or  extensively  decayed  teeth  with  vital  pulps, 
where  any  other  type  of  porcelain  crown  would  demand  devitalization. 

(c)  Devitalized  teeth  where  any  uncertainty  exists  as  to  the  healthy 
condition  of  the  roots,  which  condition   might  later  make  the  easy  re- 
moval of  the  crown  an  advantage. 

(d)  Badly  eroded  or  undeveloped  teeth. 

(e)  Lower  incisors,  on  account  of  their  roots  being  small  for  dowels. 

332659 


SUMMARY  OF  ADVANTAGES 

(a)  The  saving  of  pulps,  avoiding  the  uncertainty  of  root  fillings  in 
vital  teeth  requiring  crowns. 

(fo)  The  avoidance  of  gingival  or  pericemental  inflammation,  as  fre- 
quently found  under  banded  crowns.  Gold  crowns  on  teeth  prepared  as 
for  a  porcelain  shell  cause  less  gingival  irritation  than  when  mounted  in 
the  usual  way,  but  more  than  the  porcelain. 

(c)  Appearance.     No   other   artificial   crown   presents   so   natural   an 
appearance. 

(d)  Strength;  which  is  much  greater  than  popularly  supposed.     The 
stress  of  mastication  being  directed  against  a  larger  surface  than  when 
the  tooth  crown  has  been  cut  away  to  the  gingival,  the  root  is  more  fully 
protected  from  fracture.     The  unmounted  crown  appears  to  be,  and  is, 
very  fragile,  but  once  mounted  and  supported  at  all  points  by  the  cement 
and  stump  it  is  very  strong.    For  several  successive  years  the  same  porce- 
lain shell  mounted  on  an  extracted  root  was  driven  into  a  pine  bench-top 
as  an  illustration  to  the  students  of  the  strength  of  these  crowns  when 
mounted. 

(e)  No  danger  of  the  root  being  split  or  perforated,  as  with  dowel 
crowns. 

(f)  Limits  the  recurrence  of  caries  because  the  cement  line  is  almost 
eliminated  and  is  also  protected  by  healthy  gingival  tissue. 

(<7)  Ease  of  removal  if  necessary,  and  ease  of  replacement  if  models 
are  preserved,  as  they  should  be. 

COMPARATIVE  DISADVANTAGES 

None  but  those  due  to  the  operator's  lack  of  technical  skill  and  ex- 
perience and  the  inability  of  some  patients  to  pay  for  the  time  consumed. 

VITALITY  OF  PULP 

No  fear  need  be  felt  for  the  vitality  of  healthy  pulps  if  certain  pre- 
cautions are  carefully  observed  during  the  preparation  of  the  stump  and 
until  the  crown  has  been  finally  cemented.  Excepting  peg  laterals  and 
other  undeveloped  teeth,  teeth  requiring  single  crowns  are  usually  badly 
broken  down  by  caries  on  both  mesial  and  distal  and  part  of  the  occlusal 
surfaces.  The  resulting  cavities  have  often  been  filled  for  some  time 
previously  so  that  the  pulp  has  receded  to  a  considerable  extent.  The 
remaining  portion  of  the  stump  requires  little  more  than  the  removal  of 
the  enamel  on  the  lingual  and  labial  sides,  with  no  deep  cutting  such  as 
would  be  necessary  for  the  retention  of  fillings.  The  precautions  to  be 
taken  are  that  at  no  time  the  tooth  be  overheated  in  grinding,  especially 
when  the  work  is  done  under  an  anesthetic,  always  using  a  stream  of 


5 

water,  and  then  that,  before  dismissing  the  patient,  the  stump  be  thor- 
oughly sterilized,  varnished,  and  covered  with  cement  (not  gutta  percha) 
to  which  an  antiseptic  such  as  thymol  has  been  added. 

If  the  vital  tooth  is  in  a  conspicuous  position  in  the  mouth  a  tempo- 
rary crown  made  by  hollowing  out  a  detached  post  crown  for  the  anterior 
teeth  or  the  use  of  an  old  gold  crown  or  even  a  copper  band  filled  with 
cement  for  the  posterior  is  indicated,  as  this  serves  to  hold  away  the 
gum  from  the  ledge  lying  under  it  and  so  facilitates  the  subsequent 
cementation  as  well  as  prevents  irritation  of  the  gums  lying  over  the 
shoulder  itself.  Leaving  teeth  in  this  condition  removes  the  chief 
occasion  for  haste  in  setting  the  final  crown,  and  makes  it  possible  to 
carry  on  more  leisurely  the  necessarily  involved  laboratory  technic. 

Experience  has  shown  that  teeth  that  are  quite  sensitive  before 
cementation  of  a  porcelain  shell  soon  become  entirely  comfortable  even 
to  applications  of  cold  water,  due  to  the  very  high  insulating  properties 
of  the  porcelain. 

With  bell-crowned  bicuspids  and  molars,  it  is  frequently  unnecessary 
to  extend  the  lingual  shoulder  further  gingivally  than  to  the  greatest 
diameter  of  the  tooth,  and  in  many  other  cases  not  much  more  than  the 
enamel  is  removed. 

OPERATIVE  TECHNIC 

The  operative  technic  varies  with  the  location  of  the  tooth  in  the 
arch,  the  amount  of  tooth  substance  already  lost,  and  the  position  of  the 
adjoining  teeth.  Briefly,  the  object  is  to  reduce  the  stump  to  a  somewhat 
conical  shape,  with  its  base  toward  the  gum;  which  base  is  surrounded  by 
a  shoulder  or  ledge  about  0.5  mm.  wide  and  located  just  under  the  free 
margin  of  the  gum.  Of  course,  where  deep  cavities  exist  these  need  only 
be  cut  out  or  filled  with  cement  so  as  to  present  a  uniform  tapering  sur- 
face, toward  the  incisal  or  occlusal,  so  that  an  impression  of  the  stump 
may  be  withdrawn  without  distortion.  The  tapering  of  the  sides  is  easily 
done  with  knife-edged  stones,  Hall's  flexible  disks,  mounted  cylindrical 
stones,  chisels,  and  burs,  but  great  care  is  necessary  in  the  preparation  of 
the  shoulder.  For  this  purpose  square  and  fissure  burs  of  small  size, 
Miller's  cylindrical  stones,  safe-sided  end-cutting  burs  and  Black's 
hatchets  and  chisels  are  all  used.  The  ledge  as  well  as  the  stump  should 
be  left  with  a  surface  as  smooth  and  highly  polished  as  practicable  to 
facilitate  the  withdrawal  of  the  impression.  After  shaping  up  the  stump, 
but  before  cutting  the  ledge,  a  copper  band  approximately  as  long  as 
the  adjoining  teeth,  or  at  least  longer  than  the  stump,  should  be  fitted 
fairly  closely  and  shaped  to  firm  contact  with  the  proximate  teeth,  care- 
fully festooning  out  for  the  curvature  of  the  gum.  One  of  the  manu- 


6 


factured  copper  bands  used  for  seamless  crown  work  can  usually  be 
found  suitable  for  this  purpose. 

After  the  stump  is  prepared,  the  copper  band  is  filled  with  perfection 
modeling  compound,  thoroughly  softened  in  hot  water  and  pressed  over 
the  tooth.  Two  syringes,  one  with  cold  and  one  with  hot  water,  should 
be  ready.  As  the  compound  chills,  a  stream  of  warm  water  is  thrown 
upon  it,  keeping  it  soft  until  it  has  pressed  the  gum  away  to  take  the 
impression  of  the  root  beyond  the  shoulder.  The  band  may  be  removed 
for  examination,  but  if  this  be  done  it  is  again  warmed  with  hot  water 
when  replaced  on  the  tooth  and  forced  up  a  little  farther  than  before. 

Now,  hold  the  compound  firmly  in  position  and  chill  with  the  cold- 
water  syringe.  Any  excess  of  compound  forced  over  the  sides  of  the 
band  either  gingivally  or  incisally  is  now  removed  and  the  assistant 
directed  to  continue  dropping  cold  water  on  the  impression  while  a  bridge 


Fig.  1 


impression  tray  is  being  filled  with  plaster  mixed  with  cold  water  and  an 
excess  of  salt.  A  plaster  impression  of  the  copper  band  in  position  and 
of  the  adjacent  teeth  is  now  taken  and  removed  as  soon  as  brittle,  before 
the  heat  caused  by  the  setting  plaster  has  softened  the  modeling  com- 
pound. The  copper  band  will  usually  remain  on  the  tooth.  It  is  again 
chilled,  then  removed,  and  a  wax  bite  is  taken. 

The  next  step  is  the  selection  of  the  proper  colors  of  porcelain.  When 
the  adjoining  teeth  can  be  matched  from  a  sample  of  one  of  the  manu- 
facturer's guides,  this  is  all  that  is  necessary,  but  when  this  cannot  be 
done  the  color  most  nearly  correct  should  be  chosen  and  a  memorandum 
made  as  to  such  changes  as  may  be  demanded.  The  temporary  crown, 
before  suggested,  is  now  set  with  a  temporary  cement  and  the  patient 
may  be  dismissed.  I  usually  allow  one  hour  for  the  operative  technic 
just  outlined. 

It  is  an  advantage  in  putting  porcelain  crowns  on  many  molars,  par- 
ticularly uppers,  where  the  roots  diverge  to  a  considerable  extent,  to  be 


able  to  insert  the  necessary  dowels  without  running  the  risk  of  root 
perforations,  or  weakening  them  by  attempting  to  make  the  canals 
parallel.  This  is  easily  avoided  by  setting  dowels  in  the  individual  canals 
with  cement,  allowing  them  to  extend  to,  and  their  ends  to  meet,  well 
outside  the  pulp  chamber  as  shown  by  the  radiograph.  See  Figure  1.  The 
pulp  chamber  is  then  slightly  undercut  and  packed  with  amalgam,  which 
is  also  carried  up  around  the  dowels  to  give  them  some  conical  or  pyra- 
midal form.  From  this  point  the  procedure  is  as  for  a  porcelain  shell. 
Occasionally  pulp  chambers  are  so  deep  and  the  tooth  so  strong  that 
little  more,  if  any,  attachment  is  needed  than  the  amalgam  alone. 

At  a  subsequent  sitting,  after  the  amalgam  has  set,  the  impression  is 
taken  and  the  crown  made  as  for  a  porcelain  shell. 

If  it  ever  becomes  necessary  to  remove  a  crown  of  this  type  it  is  easily 
done  by  cutting  a  groove  in  the  porcelain  with  a  knife-edge  stone  and 
splitting  it.  The  amalgam  can  now  readily  be  drilled  out  and  the  round 
tapering  dowels,  whose  ends  protrude  from  the  pulp  chamber,  be  removed 
separately  with  pliers. 


IMPRESSIONS  FOR  OTHER  TYPES 

The  only  variation  from  this  method  when  taking  an  impression  for 
dowel  crowns  is  that,  instead  of  filling  the  copper  band  with  modeling 
compound  before  placing  on  the  root,  the  band  is  first  adjusted  to  the 
root  and  softer  compound  is  packed  firmly  into  it  with  pluggers  until  it 
has  been  forced  into  every  irregularity  and  well  into  the  root  or  pulp 
chamber.  It  is  now  chilled.  A  root  plugger  smaller  than  the  root  canal 
as  enlarged  for  a  dowel  is  heated  in  the  flame  and  used  as  an  explorer  to 
find  the  canal  openings  prepared  for  one  or  more  dowels.  The  previously 
fitted  dowels  are  now  warmed  in  the  flame  and  pressed  home  through 
these  openings.  In  going  to  their  proper  position,  they  will  carry  with 
them  compound  so  that  an  accurate  impression  of  the  root  canal  is  taken 
as  well.  After  chilling,  the  plaster  impression  is  taken  as  before.  Upon 
the  amalgam  model  made  from  this  impression,  any  type  of  crown  desired 
may  be  constructed,  and  made  to  fit  more  accurately  than  if  the  work 
were  all  performed  in  the  mouth,  as  shown  by  the  models.  If  through 
breakage  of  the  porcelain,  decay  of  the  root,  lack  of  contact,  recession  of 
the  gum,  change  of  color,  or  other  causes,  it  becomes  necessary  to  replace 
the  porcelain  of  a  dowel  crown  when  the  dowel  is  firmly  anchored  in  the 
root,  the  root  is  prepared  as  desired  without  removal  of  the  dowel,  which 
should,  however,  be  made  slightly  tapering  by  grinding,  or  by  the  addi- 
tion of  cement  or  amalgam.  The  impression  is  taken  exactly  as  for  a 
porcelain  shell.  The  laboratory  procedure  will  be  shown  later. 


8 

M.  O.  D.  CAVITIES 

To  take  an  impression  of  an  M.  O.  D.  cavity  in  a  bicuspid  or  molar, 
the  copper  band  is  fitted  roughly  and  trimmed  away  so  that  it  will  not 
pass  farther  gingivally  on  the  labial  or  lingual  surface  than  the  greatest 
diameter  of  the  tooth.  Care  should  be  taken  to  see  that  the  copper  band 
presses  close  against  the  contact  points  of  the  proximate  teeth.  To  take 
the  impression,  the  band  is  placed  in  position  and  soft  compound  forced 
in  with  pluggers,  while  a  stream  of  water  is  syringed  onto  the  tooth, 
sufficiently  hot  to  keep  the  compound  soft  and  workable.  A  small  piece 
of  compound  is  added  to  take  the  occlusal  surfaces  of  the  adjoining  teeth, 
the  whole  chilled  and  removed  without  taking  a  plaster  impression.  A 
small  wax  bite  should  be  obtained. 

As  shown  by  the  models,  from  this  small  and  quickly  obtained  impres- 
sion accurate  models  may  be  made  that  will  show  perfectly  the  cavity 
and  tooth  in  amalgam,  and  the  occlusal  and  contact  points  in  plaster.  The 
amalgam  may  be  removed  from  or  replaced  in  the  plaster  model  at  will, 
making  the  formation  and  withdrawal  of  a  wax  pattern  a  simple  and 
accurate  procedure.  The  gold  casting  may  be'  forced  into  the  model  by 
placing  it  in  the  swaging  device  and  swaging,  and  the  inlay  closely  fin- 
ished and  polished  while  on  the  model,  resulting  in  a  much  better  fit  than 
can  possibly  be  obtained  by  working  directly  on  the  tooth. 

A  little  experience  will  soon  suggest  ways  of  taking  impressions  of 
any  cavity  where  a  model  would  be  an  advantage,  but  one  fact  should 
be  strongly  emphasized,  namely,  that  in  order  to  get  an  accurate  impres- 
sion with  modeling  compound  the  material  must  be  worked  while  thor- 
oughly softened,  and  must  be  confined  with  some  sort  of  matrix,  such  as 
a  copper  band,  so  that  it  cannot  escape  when  packed  in  under  heavy 
pressure.  This  cannot  be  accomplished  through  the  use  of  small  cavity 
impression  trays. 

BRIDGES 

In  the  construction  of  bridges,  a  plaster  impression  of  the  copper  band 
— modeling  compound  impressions  of  the  abutments  may  be  taken  to- 
gether and  the  models  made  therefrom  so  handled  in  the  laboratory  that 
no  further  impressions  are  necessary,  the  bridge  being  completed  on  the 
original  models.  Where  inlay  abutments  are  to  be  used  there  is  far  less 
danger  of  error  in  replacing  the  copper  bands  in  the  plaster  impression 
than  in  replacing  the  inlays  in  a  plaster  impression  taken  while  they  are 
in  the  teeth.  Another  advantage  of  working  on  the  amalgam  models  is 
that  the  assembled  bridge  may  be  removed  for  soldering  and  replaced  on 
the  models  to  be  adjusted  and  finished.  If  any  shrinkage  or  warpage  has 
taken  place,  or  the  abutments  are  so  far  out  of  parallel  that  the  bridge 
will  not  go  to  place,  it  is  quite  evident  at  this  time  and  can  be  corrected 
or  plans  made  for  a  proper  change  in  the  abutments. 


9 

PORCELAIN  INLAYS 

Amalgam  models  are  especially  indicated  in  porcelain  inlay  work  in 
labio-gingival  cavities.  The  gum  is  easily  forced  away  by  the  modeling 
compound  and  so  a  clear  field  of  operation  is  obtained  on  the  resulting 
model. 

In  complicated  cavities  where  the  burnishing  of  a  matrix  is  a  difficult 
operation,  it  may  be  greatly  simplified  by  a  combination  of  burnishing 
and  swaging  on  an  amalgam  model.  In  fact,  the  rule  holds  good  that  the 
more  difficult  the  operation  of  making  an  inlay  or  a  crown  in  the  mouth, 
the  greater  the  necessity  for  a  correct  laboratory  model;  and  after  ten 
years'  experience  in  developing  and  using  this  technic  I  can  assure  you 
that  a  little  time  spent  in  getting  correct  impressions  is  well  repaid  in 
the  ease  and  certainty  of  subsequent  procedures.  For  those  having  a 
laboratory  assistant  much  time  is  saved,  the  laboratory  steps  becoming 
mere  routine;  and  any  competent  office  nurse  can  soon  become  quite  pro- 
ficient in  the  making  of  the  amalgam  and  plaster  models. 

To  SUMMARIZE 

The  important  points  to  be  observed  in  taking  cavity  or  root  impres- 
sions are: 

1.  When  inlay  or  crown  is  to  have  contact  with  proximate  teeth,  the 
copper  band  must  be  firmly  in  contact  with  the  contact  points  of  these 
teeth. 

2.  The  compound  should  always  be  soft  for  taking  impressions  and  al 
ways  chilled  when  being  handled  at  other  times. 

3.  All  excess  should  be  trimmed  away  so  that  overhanging  particles 
will  not  stick  to  the  plaster  impression. 

4.  The  compound  must  always  be  thoroughly  confined  by  a  matrix. 

LABORATORY  TECHNIQUE 

This  method  was  developed  with  the  idea  of  having  as  much  of  the 
work  as  possible  done  in  the  laboratory,  either  personally  or  by  an  as- 
sistant. In  the  laboratory  there  is  no  fussy  patient  to  annoy;  no  bleed- 
ing gums  to  bother;  in  fact,  no  gums  at  all,  because  they  may  be  trimmed 
away  from  the  plaster  model  or  the  amalgam  model  removed  entirely;  as 
much  time  as  necessary  may  be  used,  at  odd  times  if  more  convenient; 
and,  as  will  be  shown,  it  is  possible  to  do  everything  that  can  be  done  in 
the  mouth  with  greater  ease,  greater  comfort  and  much  more  accuracy 
in  the  laboratory.  If  a  failure  results  it  is  much  easier  to  correct  (unless 
it  occur  in  the  impression  or  model),  making  an  extra  visit  of  the  patient 
unnecessary.  The  time  used  in  obtaining  the  models  is  more  than  made 
vi p  in  the  following  procedures: 


10 


CONSTRUCTION  OF  MODELS 

The  construction  of  the  models  is  divided  into  the  following  steps, 
which  should  be  followed  out  exactly  as  outlined  for  porcelain  shell 
crowns.  Variations  for  inlay  and  dowel  crowns  will  be  mentioned  later. 

1.  Assemble  and  varnish  plaster  models. 

2.  Fill  copper  band  with  moldine  form  approximately  as  amalgam  is 
wanted,  which  should  be  as  shown  by  Figure  2. 

3.  Invest  copper  band  containing  moldine  in  plaster  by  setting  moldine 
on  glass  slab  or  other  smooth,  flat  surface  and  covering  the  whole  with 
small  mix  of  plaster. 


MOLDINE   FORM 

/N 

COMPOUND 


Moldine 


Sand 


Fig.  2 

4.  When  plaster  has  set,  pick  and  wash  out  moldine  and  pack  amalgam 
in  its  place.     This  step  is  not  easy.     The  first  application   of  amalgam 
should  be  quite  soft  and  carefully  rubbed  into  all  parts  of  the  impression 
in  small  pieces  with  smooth  pluggers.     As  soon  as  the  impression  face  is 
covered,   drier  amalgam  is  heavily  packed  with  as  large  serrated  plug- 
gers as  can  be  used,  up  to  the  level  of  the  opening  in  the  plaster,  and 
set  away  to  harden  (Figure  8). 

5.  When  the  amalgam  has  set,  cut  away  the  plaster  investment,  using 
care  not  to  disturb  or  mar  the  modeling  compound,  and  trim  the  amalgam 
model  so  that  the  bottom  is  perfectly  flat  and  smooth,  so  that  the  sides 
of  the  base  have  no  undercuts  and  the  base  is  wedge-shaped  with  its 
greatest   width   labially,   and  pyramidal   with   its  base   downward.      The 
form  just  described  should  have  been  outlined  by  the  moldine  first  placed 
in  the  copper  band.     The  base  should  also  be  highly  polished  on  all  sides. 


11 


6.  Place   copper   band   now   filled   with   amalgam   in   place   in   plaster 
impression. 

7.  Bun  plaster  model  and  when  set,  separate  impression,  warm  copper 
band  and  remove  it  together  with  the  compound. 

8.  Adjust  wax  bite  and  model  on  articulator  and  varnish  both  model 
and  the  occluding  teeth.    We  now  have  a  ' '  master  model, ' '  that  is,  a  per- 
fect reproduction  of  the  tooth  to  be  crowned  and  the  adjoining  teeth. 

9.  Take  plaster  or  modeling  compound  impression  (plaster  preferred) 
of  the  "master  model"  and  also  wax  bite,  with  the  amalgam  model  in 
place. 


PACKED 
JN   /MPRESS/ON  • 


Fig.  3 


10.  Eemove  amalgam  model  by  sliding  out  labially,  the  plaster  having 
been  cut  away  for  this  purpose,  and  place  it  in  the  plaster  impression, 
varnish  and  make  "working  model"  and  bite.     Mount  on  an  articulator 
as  before. 

11.  Remove  the  amalgam  model  as  before  and  adapt  by  burnishing 
and  swaging  a  platinum  matrix  of  1/1000  foil,  carrying  the  foil  half  way 
down  the  sides  of  the  pyramidal  base. 

12.  Place  the  model,  with  the  matrix  in  position,  on  a  glass  slab  and 
cover  with  plaster. 

13.  When  the  plaster  has  set,  remove  the  amalgam  with  sticky  wax 
and  fill  the  platinum  matrix  with  ahmdum  cement.     Before  packing  the 
alundum  cement,  a  small  edge  of  the  platinum  foil  is  turned  in  from  the 


12 


Plaster     f-Q/L  MATRIX   /Nl/ESTED 


Fig.  4 


plaster  so  that  it  will  be  firmly  imbedded  in  the  cement.  Finally,  insert 
a  round  iridio-platinum  wire,  about  17  gauge,  in  the  center  of  the  base, 
allowing  it  to  protrude  about  one-eighth  of  an  inch  (Figure  4). 

14.  Dry  immediately,  if  necessary,  but  slowly  over  a  bunsen  burner, 
finally  bringing  up  to  a  red  heat  with  the  blowpipe.  If  there  is  no  hurry, 
allow  the  cement  to  dry  before  applying  heat.  Then  remove  the  plaster 
and  bake  the  platinum-covered  alundum  model  in  an  electric  furnace  at 
approximately  2600°  F.  We  now  have  a  foil-covered  alundum  model  that 
has  a  wire  firmly  imbedded  in  it  for  ease  of  handling  in  the  pin  vise 
and  furnace,  and  that  will  fit  both  the  "master"  and  the  "working" 


FO/L  COVERED  ALUNDUM  MODEL 
Fig.  5 


13 

model,  when  a  slot  is  made  in  the  plaster  to  receive  the  wire  (See  Figure 
5).  The  contacts  of  the  proximate  teeth  on  the  working  model  are  now 
cut  away  to  allow  for  shrinkage  of  the  porcelain,  approximately  one- 
fifth  of  the  mesio-distal  diameter  of  the  finished  crown.  After  each 
baking  the  alundum  base  and  crown  are  tried  on  the  ' '  master  model ' ' 
for  guidance  as  to  the  exact  contact. 

When  the  crown  is  finally  baked,  the  iridio-platinum  pin  is  removed 
from  the  base  with  pliers,  and  the  alundum  is  removed  by  grinding  out 
with  small  stones,  under  water.  It  can  be  dissolved  out,  or  at  least 
softened,  by  the  addition  of  one  drop  of  hydrofluoric  acid  left  in  the 
crown  for  five  minutes,  the  outer  surface  being  first  covered  with  wax 
for  protection. 

The  impression  obtained  of  a  root  containing  a  dowel  already  set  is 
handled  in  the  laboratory  exactly  like  a  porcelain  shell  except  that  if  the 
crown  end  of  the  dowel  be  round  it  is  easier  and  will  be  stronger  if  its 
place  in  the  impression  be  filled  with  a  German  silver  wire  of  the  proper 
size,  allowing  it  to  extend  into  the  amalgam. 


LABORATOEY  TECHNIQUE  FOE  DOWEL  CEOWNS   WITH 
CAST  METAL  BASES 

The  first  variation  from  the  porcelain  shell  technic  is  in  the  applica- 
tion of  the  moldine  to  the  root  impression  for  the  formation  of  a  plaster 
matrix  or  form,  into  which  the  amalgam  is  packed  to  make  the  model. 

In  these  cases,  one  or  more  dowels  are  present,  necessitating  a  deeper 
model,  and  while  the  porcelain  shell  model  was  formed  with  a  view  to  its 
exact  duplication  in  alundum,  this  step  is  not  required  nor  is  but  one 
plaster  model,  because  it  will  not  be  necessary  to  trim  or  mutilate  it,  to 
allow  for  shrinkage  of  the  porcelain  body.  Therefore,  instead  of  making 
the  amalgam  model  pyramidal  with  the  base  down,  we  make  it  pyramidal 
with  the  base  up;  in  other  words,  tapering  toward  the  root  end.  This 
model  is  removed  from  the  impression  occlusally  by  drilling  a  small  hole 
through  the  plaster  opposite  the  root  end,  and  gently  prying  the  model 
out  (See  Figure  6). 

A  few  suggestions  will  be  offered  as  to  accurately  adapting  the  cast 
base  of  a  manufactured  porcelain  tooth  of  any  suitable  kind: 

1.  Grind  the  porcelain  to  shape,  arranging  for  a  shoulder  at  least  as 
high  as  the  contact  points  on  the  mesial,  distal  and  lingual  sides  of  the 
tooth  if  a  bicuspid  or  molar.  This  will  form  a  box  in  the  casting  to  sup- 
port the  porcelain  and  provide  an  easy  means  to  add  to  the  contact 
points  if  necessary  by  the  addition  of  a  little  solder. 


2.  Swage  a  matrix  of  1/1000  platinum  foil  over  the  root,  forming  a 
band,  if  desired,  and  insert  the  dowel  or  dowels  in  their  proper  positions, 
fastening  them  with  a  little  sticky  wax. 

3.  Swage  a  similar  foil  matrix  over  the  porcelain;  place  softened  in- 
lay  wax   on   the   root   while   on   the   model   and   set   porcelain   in   proper 
position. 

4.  Remove  the  amalgam  model  and  finish  wax  in  desired  form. 

5.  Eemove  waxed-up  crown  from  the  amalgam  model — lift  out  porce- 
lain and  paint  both  exposed  surfaces  of  platinum  with  a  thin  mixture  of 
whiting  in  alcohol. 

6.  Invest  and  cast  into  a  hot  mold  so  that  the  gold  will  flow  readily 
around  the  dowels. 


f?OOT  rORM 

oo iv EL 


Fig.  6 


Variations  for  other  types  of  crowns  suggest  themselves,  the  funda- 
mental steps  for  obtaining  fit  and  adaptation  being  identical. 


LABORATORY  TECHNIC  FOR  M.  O.  D.  CAST  INLAYS 

The  amalgam  model  base  is  first  shaped  as  for  the  dowel  crown.  Plas- 
ter is  now  poured  into  the  impression  of  the  occlusal  surfaces  of  the  ad- 
joining teeth  and  closely  against  the  sides  of  the  copper  band,  which  you 
will  remember  was  in  close  contact  with  the  contact  points  of  the  proxi- 
mate teeth.  This  establishes  the  mesio-distal  diameter.  After  removing 
the  band  and  compound  the  little  wax  bite  is  adjusted  and  poured.  After 
separation  we  now  have  a  model  correctly  showing  contact  and  occlusion. 
Fill  the  cavity  with  inlay  wax,  carve,  invest  and  cast  the  fillings. 

It  is  unusual  for  one  of  these  castings  to  go  readily  into  place,  in  fact 
almost  impossible  without  spreading  the  filling  a  trifle  at  the  gingival. 
After  removing  any  apparent  roughness  on  the  cavity  side  of  the  inlay, 
place  it  in  the  model,  mount  in  the  swaging  device  and  drive  to  place 


15 

with  unvulcanized  rubber.  After  trying  in  the  tooth  and  ascertaining 
if  there  is  any  deviation  from  the  amalgam  model,  there  being  none,  the 
inlay  may  be  burnished,  finished  and  polished  on  the  model  more  ad- 
vantageously than  in  the  mouth,  especially  at  the  gingival  margin. 

PORCELAIN  TECHNIQUE  BODIES 

During  the  past  few  years  so-called  low  fusing  porcelains,  meaning 
those  porcelain  bodies  that  will  fuse  in  five  minutes  below  the  melting 
point  of  pure  gold,  have  gradually  been  abandoned  by  many  practitioners 
for  so-called  high  fusing  bodies  that  require  a  platinum  rather  than  pure 
gold  base  upon  which  to  fuse  the  material.  More  recently  still  the  ten- 
dency is  to  raise  the  fusing  point  farther,  so  that  while  a  short  time  ago 
a  porcelain  body  fused  at  2300°  F.  was  considered  high  fusing,  now  bodies 
fusing  in  a  few  minutes  around  2600°  F.  are  in  common  use. 

These  higher  fusing  bodies  are  apparently  stronger,  shrink  less  in 
firing  and  are  much  more  transparent  and  life-like  in  appearance.  There 
is  also  less  liability  to  over-fuse  and  great  permanence  of  color  is  there- 
fore to  be  expected.  There  are  no  unusual  difficulties  connected  with 
their  manipulation,  excepting  the  strain  on  the  electric  furnace.  Through 
changes  in  the  construction  of  furnaces,  such  as  the  addition  of  larger 
resistors  and  the  development  of  muffle  and  investing  materials  of 
greater  purity,  it  is  probable  that  the  manufacturers  will  keep  up  with 
the  procession  and  supply  us  with  our  needs  in  this  direction.  With  our 
present  furnace  a  great  deal  can  be  done  to  save  the  muffle  winding 
by  using  a  heavy  insulated  door,  such  as  is  supplied  with  the  Hammond 
furnace,  keeping  the  opening  closed  as  much  as  possible  when  baking  at 
high  temperatures  and  allowing  a  little  more  time  rather  than  great  heat 
to  do  the  baking.  It  is  quite  possible,  but  impracticable,  to  fuse  so- 
called  2600°  F.  porcelain  on  pure  gold  if  given  enough  time. 

FOUNDATION  BODIES  AND  ENAMELS 

Crowns  made  under  this  method  are  finished  in  two  or  three  bakes, 
and  the  natural  shrinkage  of  the  porcelain  is  perfectly  controlled  with- 
out the  use  of  bodies  of  different  fusing  points,  so  that  the  use  of  an 
enamel  body  is  eliminated  except  in  cases  where  an  addition  is  to  be 
made  after  the  platinum  matrix  has  been  removed. 

SHRINKAGE  AND  DENSITY 

Shrinkage  and  density  are  closely  related,  the  former  depending  to  a 
great  degree  upon  the  latter.  Dense  porcelain  is  to  be  obtained  only  by 
the  observance  of  certain  rules. 

1.  The  body  should  be  well  spatulated  to  a  thick  creamy  consistency 
;iml  ;is  much  air  as  possible  rubbed  out. 


16 

2.  It  should  be  applied  to  the  work  in  small  amounts,  each  application 
being  thoroughly  condensed  before  more  is  added. 

3.  The  work  should  be  carried  forward  steadily,  always  remembering 
that  dry  body  is  not  necessarily  dense  body  and  that  the  moisture  dries 
out  very  rapidly  in  the  air  without  the  application  of  other  means  of 
absorption. 

In  carved  crown  work,  burnishing  or  ironing  the  body  into  form  is 
better  practice  than  to  attempt  any  extensive  jarring  to  produce  den- 
sity. The  alundum  bases  are  quite  absorbent.  Therefore  they  should 
first  be  moistened  with  a  drop  of  water  before  any  body  is  applied,  to 
prevent  too  rapid  drying. 

OBTAINING  COLOR 

All  crowns  contain  some  proportion  of  yellowish  hues,  and  most  crowns 
can  be  made  by  the  combination  and  blending  of  the  proper  hue  of  yellow 
with  one  other  color.  To  obtain  the  selection,  analyze  the  tooth  taken 
from  the  guide  by  comparing  its  different  sections  with  the  color  guide  of 
the  body  to  be  used  and  make  the  proper  choice.  Now  apply  the  yellow, 
building  up  the  tooth  approximately  like  the  dentine  and  cover  with  the 
second  body  as  an  enamel,  allowing  them  to  overlap  and  blend  at  the 
right  place.  After  the  crown  is  built  up  in  more  or  less  block  shape,  it 
is  carved  to  form  and  occlusion.  Dry  out  and  bake. 

More  particular  details  as  to  the  handling  of  the  porcelain  will  be 
gone  into  during  the  laboratory  periods.  Charts  will  also  be  displayed 
giving  an  analysis  of  certain  color  guides,  but  these  are  considered  as 
being  of  little  benefit  to  the  operator  who  has  an  eye  for  color;  and  he 
who  has  not  would  better  serve  his  patients  by  not  attempting  porcelain 
work. 

METHOD  OF  USING  A  FACING 

This  method  is  simple  and  appeals  particularly  to  the  inexperienced, 
but  only  in  exceptionally  favorable  cases  does  it  produce  a  crown  of  as 
fine  appearance  as  the  hand-carved.  One  of  the  chief  factors  adding  to 
the  lifelike  appearance  of  the  hand-carved  porcelain  shell  is  found  in 
its  very  imperfections  of  form,  whether  caused  intentionally  or  otherwise, 
and  these  imperfections  are  never  found  in  manufactured  teeth.  An- 
other disadvantage  in  the  use  of  facings  for  a  porcelain  shell  on  vital 
teeth,  where  the  labial  plate  is  necessarily  quite  thin,  is  that  the  colors 
of  a  facing  are  blended  by  laying  one  color  over  another,  so  that  in 
grinding  out  the  facing  to  great  thinness  most  of  the  underlying  color 
is  ground  away  and  there  is  no  opportunity  for  strengthening  it  by 
further  additions. 

If,  however,  a  favorable  case  presents  itself,  the  facing  of  any  kind 
suitable  is  ground  away  on  the  back  until  it  will  permit  of  adjustment 
to  the  labial  contour,  particular  care  being  taken  to  let  it  rest  against 


17 

the  stump  and  on  the  labial  gingival  ledge  j,t  some  point,  fastening  it  in 
position  by  cementing  it  to  the  base  at  the  labial  gingival  with  sticky 
wax.  Now  add  the  body  to  the  lingual,  making  the  first  application  thin 
and  jarring  down  until  the  body  has  been  thoroughly  packed  under  the 
facing  around  the  labial  ledge  and  in  all  places  inaccessible  for  burnish- 
ing. The  building  up  and  carving  now  goes  forward  as  in  a  carved 
crown,  using  drier  porcelain.  Before  insertion  in  the  furnace  most  of 
the  wax  used  to  hold  the  facing  in  position  temporarily  is  removed  with 
a  hot  spatula.  The  rest  will  be  readily  burned  away  without  injury  to 
the  porcelain,  and  the  crown  from  here  on  is  handled  in  the  usual  manner. 

ALUNDUM 

Alundum  is  a  refractory  material  made  by  fusing  the  mineral  bauxite, 
a  natural  hydrate  of  alumina,  or  a  pure  aluminum  oxide,  in  an  electric 
furnace  of  the  arc  type.  Until  the  invention  of  the  process  for  the  manu- 
facture of  alundum,  bauxite  was  considered  infusible.  Most  of  the  im- 
purities found  in  bauxite  are  removed  by  certain  processes  of  puri- 
fication. 

The  manufacturers  give  it  a  melting  point  of  2050°  centigrade  (3722° 
F.)  and  that  of  bonded  alundum,  or  alundum  cement,  as  slightly  below 
this.  The  thermal  conductivity  of  bonded  alundum  is  stated  as  being 
2.1  times  that  of  ordinary  fire  brick,  and  1.6  times  that  of  chemical  porce- 
lain; hence  its  great  value  in  electric  furnace  muffles. 

The  alundum  cement  used  in  this  work  is  alundum  to  which  a  ceramic 
binder  has  been  added.  A  mass  the  size  of  a  molar  tooth  shows  no  shrink- 
age or  expansion.  Porcelain  may  be  baked  directly  on  it  without  any 
injury  to  the  porcelain  whatsoever,  but  after  fusing  they  are  very  diffi- 
cult to  separate. 

The  cement,  which  comes  as  a  dry  powder,  is  mixed  with  water  to  the 
consistency  of  thick  mud.  It  is  better,  but  not  necessary,  to  allow  it  to 
dry  before  applying  heat.  It  is  not  real  cement  because  it  does  not  set 
until  considerable  heat  is  applied,  vitrification  taking  place  at  about 
1000°  C. 

Alundum  cement  forms  to  be  used  in  porcelain  work  should  be  previ- 
ously baked  to  the  fusing  point  of  the  porcelain  so  that  any  gases  that 
might  be  formed  at  the  higher  temperature  be  first  driven  off. 

The  cement  is  valuable  for  investing  the  platinum  matrix  for  a  porce- 
lain inlay,  as  it  will  thoroughly  control  shrinkage  and  preserve  its  form 
while  applying  and  baking  the  porcelain,  and  for  making  small  stands 
to  support  work  while  in  the  furnace.  After  repeated  firings,  but  within 
certain  limitations,  it  becomes  harder. 

Of  the  different  grades  manufactured  by  the  Norton  Company  of 
Worcester,  Massachusetts,  the  one  known  as  R.A.  162  is  the  only  one  I 
have  tested  that  answers  all  our  requirements. 


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